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� I <br /> San Joaquin County <br /> ° '" DIRECTOR <br /> Environmental Health Department <br /> .cp Donna Heran,REHS <br /> 1868 East Hazelton Avenue <br /> a. A PROGRAM COORDINATORS <br /> Stockton, California 95205-6232 <br /> Robert McClellon, REHS <br /> Jeff Carruesco, REHS,RDI <br /> !` Kasey Foley,REHS <br /> 6q —. �P Website: www.sjgov.org/ehd <br /> �r r=°a,vl Linda Turkatte,REHS <br /> Phone: (209) 468-3420 Rodney Estrada,REHS <br /> Fax: (209)464-0138 Adrienne Ellsaesser, REHS <br /> August 19, 2014 <br /> Chevron Environmental Management Company <br /> c/o Brian Waite, PG <br /> 6101 Bollinger Canyon Road, BRIX-5321 <br /> San Ramon, California 94583 <br /> Subject: Former Unocal No. 0187 <br /> Chevron Site No. 306415 <br /> 437 East Miner Avenue <br /> Stockton, California 95202 <br /> Dear Mr. Waite: <br /> The San Joaquin County Environmental Health Department (EHD) has received and reviewed <br /> Work Plan for Well Destructions (work plan), dated 17 June 2014, prepared by your consulting <br /> firm, ARCADIS U.S. Inc. (ARCADIS), on your behalf for the above-referenced site. The EHD <br /> had directed by letter dated 24 February 2014, the submittal of a scope of work proposal that <br /> detailed the condition and construction of the wells and the methods and materials to be used to <br /> destroy the wells. <br /> In the work plan, ARCADIS proposes to destroy off-site groundwater monitoring wells (U-7, U-8, <br /> U-9, U-11, U-16, U-18, U-20, U-23) and soil vapor probes (SVP-1A through SVP-8A and <br /> SVP-1B through SVP-8B) by pressure grouting. ARCADIS proposes to apply twenty-five <br /> pounds per square inch (psi) of pressure to the cement grout inserted into the casing for five <br /> minutes prior to excavating around each casing to a depth of three feet below surface grade <br /> (bsg), then cutting off the casing six inches above the bottom of the excavation and adding <br /> additional cement grout to form a 'mushroom cap'. <br /> ARCADIS proposes to destroy the remaining remediation and on- and off-site monitoring wells <br /> by detonation techniques as follows: <br /> • Subcontract the well destructions to Welenco, a licensed explosive contractor; <br /> • Apply explosive detonator cords with charges set at depths of each well screen interval, <br /> prior to inserting neat cement grout into the well casing from total depth to surface using <br /> a tremie pipe; and <br /> • Detonate the charges and once completed, backfill the open casing with neat cement <br /> grout, forming a 'mushroom cap' at three feet bsg with a diameter one-foot larger than <br /> the original borehole, as described above. <br />